Method and apparatus for communicating to UE an indication of available RS, based on MIMO mode settings

ABSTRACT

The present solution ensures that the UEs are able to make use of all the available reference signals that can be used in a cell for performing UE measurements, estimations or demodulations. That is achieved by indicating on a downlink common or shared channel, the MIMO mode settings associated with a specific network node. The indicated MIMO mode settings explicitly or implicitly indicate available common reference signals and/or dedicated reference signals to be used for said UE measurements, estimations or demodulations, which implies that measurements, estimations or demodulations can be performed based on said received indication.

RELATED APPLICATIONS

This application is a reissue application of U.S. application Ser. No.15/607,010, filed May 26, 2017, and issued as U.S. Pat. No. 10,278,085,which is a continuation of U.S. application Ser. No. 14/540,780, filedNov. 13, 2014, and issued as U.S. Pat. No. 9,693,247, which is acontinuation of U.S. application Ser. No. 12/867,494, filed Aug. 13,2010, now U.S. Pat. No. 8,917,696, which was the National Stage ofInternational Application No. PCT/SE2009/050084, filed Jan. 28, 2009,which claims the benefit of U.S. Provisional Application No. 61/028,662,filed Feb. 14, 2008. The disclosures of each of these applications areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a method and arrangement in atelecommunication system, in particular to enable the UE to performaccurate measurements, estimations or demodulations.

BACKGROUND

UTRAN (Universal Terrestrial Radio Access Network) is a term identifyingthe radio access network of a UMTS (Universal Mobile TelecommunicationsSystem), wherein the UTRAN consists of Radio Network Controllers (RNCs)and NodeBs i.e. radio base stations. The NodeBs communicate wirelesslywith mobile user equipments (UEs) and the RNCs control the NodeBs. TheRNCs are further connected to the Core Network (CN). Evolved UTRAN(E-UTRAN) is an evolution of the UTRAN towards a high-data rate,low-latency and packet-optimised radio access network. Further asillustrated in FIG. 1 , the E-UTRAN consists of radio base stations(eNBs) 12, and the eNBs are interconnected and further connected to theEvolved Packet Core network (EPC) 14. E-UTRAN is also being referred toas Long Term Evolution (LTE) and is standardized within the 3^(rd)Generation Partnership Project (3GPP). FIG. 1 also shows UEs 10 incommunication with the eNBs 12.

E-UTRAN is a pure packet data designed cellular system, in whichtransmissions of user data in uplink and downlink always take place viashared channels. Orthogonal Frequency Division Multiplexing (OFDM)technology is used in the downlink, whereas DFT (Discrete FourierTransform) based pre-coded OFDM is used in uplink. As similar to HSPA(High Speed Packet Access) in the UTRAN, the UE monitors physicaldownlink control channels (PDCCH) in order to access UE dedicated userdata on the physical downlink shared channel (PDSCH) and the networkassigns uplink scheduling grants to the UE on demand basis for uplinktransmission via the physical uplink control channel (PUCCH) and thephysical uplink shared channel (PUSCH). Error detection is provided ontransport blocks and control payloads through CRC, and HARQ operationsensure efficient re-transmissions.

FIG. 2 illustrates mapping of downlink common reference signals for one,two and four antenna ports.

OFDM is a modulation scheme in which the data to be transmitted is splitinto several sub-streams, where each sub-stream is modulated on aseparate sub-carrier. Hence, in OFDMA based systems, the availablebandwidth is subdivided into several resource blocks prior to beingtransmitted. A resource block is used both for uplink and downlink andis defined in both the time and the frequency domain. According to theE-UTRAN standard, a resource block size is 180 KHz (comprising of 12sub-carriers each with 15 KHz carrier spacing) and 0.5 ms (time slot) infrequency and time domains, respectively. The transmission time interval(TTI) comprises of 2 time slots, which correspond to 1 ms length intime. The radio frame is 10 ms long. The overall uplink and downlinktransmission bandwidth can be as small as 1.4 MHz and as large as 20MHz.

Each time slot comprises of N number of OFDM symbols as illustrated inFIG. 2 and a cyclic prefix (CP) is appended to each OFDM symbol toenable the mitigation of inter-symbol interference. The number of OFDMsymbols ‘N’ per slot depends upon the cyclic prefix in use. In smallcells typically normal CP (around 5 μs) is used whereas in larger cellsextended CP (around 17 μs) is used. Therefore When normal CP is usedmore OFDM symbols can be used in a slot.

Each element in the time frequency resource grid for antenna port p iscalled a resource element 20, which is uniquely identified by the indexpair (k,l) in a slot represented; k^(th) sub-carrier and l^(th) OFDMsymbol as shown in FIGS. 1 and 2 .

FIG. 2 further illustrates the resource elements 24 used for downlinkcommon reference signal transmission for extended CP as specified inE-UTRA technical specification 36.211. The notation R_(p) is used todenote a resource element used for common reference signal transmissionon antenna port p. The common reference signals are also referred to ascell specific reference signal as opposed to UE specific referencesignals which are also referred to as dedicated reference signals. Asindicated in FIG. 2 , some resource elements 20 denoted by crosses arenot used for transmission on a specific antenna port.

Reference signals or pilot signals or pilot sequences or trainingsequences have similar meaning and are interchangeably used inliterature. It is standardized set of signal sequences which aretransmitted by the transmitter and are known a priori to the receiver.Their main objective is to assist the receiver to estimate thecharacteristics of radio channel, which especially varies over time dueto user mobility.

The terms reference signal or reference symbol are also interchangeablyused but they have similar meaning.

E-UTRAN utilizes multiple antennas techniques referred to as MIMO(Multiple Input Multiple Output) modes. Examples of such MIMO modes areprecoding mode and beamforming mode. Precoding mode works withcodebook-based transmission weights and utilizes common reference signalfor channel estimation. A UE can determine a codebook index from thechannel estimates and feed it back to the evolved NodeB (eNodeB).Beamforming mode works however with non-codebook based transmissionweights, which requires in the downlink a dedicated reference signalthat is precoded with the same transmission weights as the data and canbe operated without any feedback of a codebook index. UE measurementsfor radio resource management, such as mobility management, areperformed based on the common reference signals.

Regarding the dedicated reference signal patient design for thebeamforming mode, in one scenario where all the users in one cell areconfigured for beamforming mode, the shared channel is demodulated basedon the dedicated reference signal. On the other hand, common channelssuch as broadcast channel or other common control channels such asPDCCH, which may be transmitted to all or a group of UEs, are typicallysent over the entire cell. In other words they are not beamformedtowards a particular UE. Hence, the UE needs to use common referencesignals to demodulate all common channels. This means that the networkhas to transmit both dedicated and common reference signals in a cellsupporting beamforming. The transmission of dedicated reference signalsin addition to the common reference signals results in that the overalloverhead of reference signals becomes quite high.

It is therefore desired to reduce this overhead when dedicated referencesignals are transmitted to support beamforming in a cell. One way is toreduce the common reference signal density, e.g. to only keep the commonreference signals in the same OFDM symbols as the common control channelwhile still keeping the common control channel demodulation performancegood enough. In other scenarios where there are users configured for thepreceding mode within one cell, common reference signals are requiredfor both common control channel demodulation and the shared channeldemodulation. Then it is preferred that the common reference signal isspread among the whole subframe, i.e. higher density.

The common reference signals are also used by the UE to performneighbour cell measurements, which are used for taking mobilitydecisions such as cell reselection and handover. The neighbour cellmeasurements include, e.g. reference signal received power (RSRP) andreference signal received quality (RSRQ). However, the number ofavailable reference signals is reduced if e.g. beamforming is used. Aninsufficient number of reference signals may adversely impact theneighbour cell measurement performance.

Moreover, LTE supports MBSFN (Multicast Broadcast Single FrequencyNetwork) operation on the same carrier as unicast traffic. This meansthat a subset of the subframes is allocated to MBSFN transmission frommultiple cells. In such subframes the common reference signaltransmission is reduced and the common reference signals available formeasurements are only transmitted in the first symbol of each subframe.In other normal unicast subframes, the reference signals from antennaport 0 and 1 for mobility measurements are transmitted in four differentseparated subframes.

In the current LTE it is desired to use as many reference signals aspossible for neighbour cell measurements in order to achieve a goodmobility management. For this purpose the serving cell can provideneighbour cell configuration indicators to the UE on a dedicatedchannel. These indicators can be used to indicate whether or not theneighbour cells have the same configuration as the serving cell andwhether there are any MBSFN subframes at all. In this way the terminalwill be able to use as many common reference signals as possible whenperforming the measurements.

SUMMARY

However, when considering a possible reduction of the common referencesignals for more efficient support of beamforming with dedicatedreference signals, there is a risk that different cells within the samearea can use different MIMO modes with different common reference signalpatterns. This can not be reflected by the existing indicators.

Thus the object of the present invention is to provide an improvedmethod and arrangement for enabling a user equipment, UE, to performmore accurate measurements, estimations or demodulations. This isachieved by mapping beamforming information on common and sharedchannels which ensures that user equipments are able to make use of allthe available reference signals that can be used in a cell forperforming measurements, estimations or demodulations e.g. neighbourcell measurements. When performing those measurements, estimations ordemodulations, it is desired to use as many signals as possible. Thisimplies that the measurements, estimations or demodulations performedaccording to the present invention will be improved.

According to a first aspect of the present invention a method m anetwork node of a cellular communication network for enabling a userequipment, UE, to perform measurements, estimations or demodulations isprovided. In the method, MIMO mode settings associated with the networknode is determined. It is then indicated on a downlink common or sharedchannel, the determined MIMO mode settings to the UE. The indicated MIMOmode settings explicitly or implicitly indicate available commonreference signals and/or dedicated reference signals to be used for saidUE measurements, estimations or demodulations. It should be noted thatthe dedicated reference signals are used for beamforming since they areUE specific which implies that they are used by the UE for performingchannel estimation for the received beam as well as some sort ofbeamforming specific measurements e.g. channel quality indicator (CQI)which is used for scheduling. The common reference signals may be usedfor measurements, estimation and demodulation.

According to a second aspect of the present invention, a method in a UEfor enabling the UE to perform measurements, estimations ordemodulations is provided. In the method, an indication is received, ona downlink common or shared channel, of determined MIMO mode settingsassociated with a network node. The indicated MIMO mode settingsexplicitly or implicitly indicate available common reference signalsand/or dedicated reference signals to be used for said UE measurements,estimations or demodulations. Measurements, estimations or demodulationsbased on said received indication are performed accordingly.

According to a third aspect of the present invention a network node of acellular communication network for enabling a user equipment, UE, toperform measurements, estimations or demodulations is provided. Thenetwork node comprises a first unit configured to determine MIMO modesettings associated with the network node. It further comprises a secondunit configured to indicate, on a downlink common or shared channel, thedetermined MIMO mode settings to the UE, wherein the indicated MIMO modesettings explicitly or implicitly indicate available common referencesignals and/or dedicated reference signals to be used for said UEmeasurements, estimations or demodulations.

According to a fourth aspect of the present invention a UE forperforming measurements, estimations or demodulations is provided. TheUE comprises a receiver configured to receive an indication, on adownlink common or shared channel, of determined MIMO mode settingsassociated with a network node. The indicated MIMO mode settingsexplicitly or implicitly indicate available common reference signalsand/or dedicated reference signals to be used for said UE measurements,estimations or demodulations. The UE further comprises a unit configuredto perform measurements, estimations or demodulations based on saidreceived indication.

Advantages with the embodiments of the present invention are thatbeamforming information on the common control channel is transmitted,which implies that:

The UE is capable to detect the common reference signal pattern that isused in the monitored cell at very early stage. Thus, the UE can makefull use of all the reference signals to demodulate downlink controlsignaling such as PDCCH.

The UE is capable to detect (or is informed about) the common referencesignal pattern that is used in the monitored cell at very early stage.Thus the UE can make full use of all the reference signals to performmeasurement for difference usages, e.g. for handover.

The UE is capable to detect whether a cell will work on beamforming modeor not, which implies that the UE knows what kind of feedback is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a mobile telecommunication network wherein theembodiments of the present invention may be implemented.

FIG. 2 illustrates mapping of downlink common reference signals(extended cyclic prefix) according to prior art.

FIG. 3 illustrates flowcharts of methods according to embodiments of thepresent invention.

FIG. 4 illustrates a UE and a network node according to embodiments ofthe present invention.

DETAILED DESCRIPTION

The present invention will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. The invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. In thedrawings, like reference signs refer to like elements.

Moreover, those skilled in the art will appreciate that the means, unitsand functions explained herein below may be implemented using softwarefunctioning in conjunction with a programmed microprocessor or generalpurpose computer, and/or using an application specific integratedcircuit (ASIC). It will also be appreciated that while the currentinvention is primarily described in the form of methods and devices, theinvention may also be embodied in a computer program product as well asa system comprising a computer processor and a memory coupled to theprocessor, wherein the memory is encoded with one or more programs thatmay perform the functions disclosed herein.

If a user equipment (UE) always assumes the worst scenario, i.e. thereduced number of common reference signals in all cells, the measurementperformance will be deteriorated implying one or more of the followingreasons: poor measurement accuracy, longer measurement period, etc. Themeasurement performance degradation due to the reduced reference signalsbecomes especially pronounced for user equipments at higher speed. Insuch cases the bias of the measurement reports becomes large such thatthe measurement quantity that is reported by the UE becomes lessreliable. The overall impact is that this will eventually affect themobility performance, e.g. handover performance, if the serving celloperates in pure beamforming mode and at least one of the neighbouringcells uses the precoding mode (or vice versa. In that case, the straightforward way for performing the UE measurements is to rely on the moresparse availability of common reference signal which occurs in thebeamforming mode.

Similar problems as described above also exist for basic channelestimation: The channel estimates based on common reference signals maybe used for demodulation of control signaling and, depending on the MIMOmode definition, demodulation of data channels, channel qualityestimation, etc. Without knowing the common reference signal pattern,demodulation of basic downlink control signaling (such as physicalbroadcast channel (PBCH), PCFICH, PHICH and PDCCH detection) can onlyrely on a more sparse common reference signal, which is known to alwaysexist independent of the MIMO mode. In the end, this leads to worseperformance in the precoding mode where more reference signals areavailable for neighbour cell measurements. In addition, beamforming modeand precoding mode require different feedbacks from the UE. Hence, MIMOmode information is needed for the UE to prepare the correct feedbacktype.

In this specification, a reference signal is any sequence of signalswhich is known to the UE a priori i.e. the pattern may be generallyspecified in the standard. The reference signals assist the UE inperforming various tasks: channel estimation, measurements, determiningcell timing etc. As stated above, there are two main types of referencesignals: common and dedicated reference signals. The common referencesignals are cell specific and common to all users in a cell and aretransmitted regardless whether users are served or not. They are usedfor channel estimation and for measurements (e.g. cell specificmeasurement i.e. neighbour cell measurement). Dedicated referencesignals are user specific i.e. activated when user is active. Thededicated reference signals are used for beamforming which implies thatthey are used by the UE for performing channel estimation for thereceived beam as well as some sort of beamforming specific measurementse.g. channel quality indicator (CQI) which is used for scheduling. So ifthe network signals dedicated reference symbols or its identity then theUE can find out the available common reference symbols because dedicatedreference symbols plus common reference symbols is constant.

The embodiments of the present invention ensure that the UEs are able tomake use of all the available reference signals that can be used in acell for performing measurements and estimations, e.g. performingneighbour cell measurements.

Hence, the present invention relates to methods and arrangements formapping or signalling MIMO mode information, e.g. information whetherbeamforming is used or not and/or information associated with the commonreference signal pattern, such as the index of the pattern or thepattern itself with the smallest number of available common referencesignals (i.e. with the highest number of dedicated reference signals).The MIMO mode information is sent on a common or shared channel or anytype of appropriate broadcast or multicast channel, e.g. PBCH. It isalso possible to map such information on the synchronization channel(PSS/SSS), on the dedicated broadcast channel (D-BCH), which is mappedon a shared channel as in LTE, or on a common reference signals. It ispossible to map the MIMO mode information on the common referencesymbols since certain minimum portion or number of common referencesignals will always be sent regardless of the density of dedicatedreference signals. The presence of minimum set of common referencesignal is required for demodulating common channels and for neighbourcell measurements as explained in more detail below. Thus when MIMO modeinformation is mapped on common reference signal it may either be in theform of a single bit indicating the presence or absence of the dedicatedreference signal, or it may be more detailed information (e.g. 4 bits)containing the index or identity of the dedicated reference signalpatient present in that cell.

In accordance with the present invention as illustrated in the flowchartof FIG. 3 , the network node, e.g. the eNode B, determines 301 MIMO modesettings associated with the network node and indicates 302, on adownlink common or shared channel, the determined MIMO mode settings toa UE. The UE may be located in a cell served by said network node or ina neighbouring cell. The indicated MIMO mode settings explicitly orimplicitly indicate available common reference signals to be used formeasurements, estimations or demodulation. The measurements, estimationsor demodulation may be neighbour cell measurement, channel estimation,demodulation and CQI estimation.

Accordingly, the UE receives 304 an indication, on a downlink common orshared channel, of the determined MIMO mode settings from a networknode, wherein the indicated MIMO mode settings explicitly or implicitlyindicate available common reference signals and/or dedicated referencesignals to be used for said UE measurements, estimations ordemodulations. Then the UE can perform 305 measurements, estimations ordemodulations based on said received indication.

According to a first embodiment of the present invention, the MIMO modeinformation is sent from the serving cell, i.e. the network node servingthe UE, and the MIMO mode information comprises information whether theserving cell uses beamforming or not. In addition, the serving cell mayalso indicate whether beamforming, is used in a neighbouring cell. Thusone bit may be used to carry this information. In this case the UE mayassume the worst case scenario in terms of the common reference signal.This means in case more than one dedicated reference signal patterns arepossible in a cell the UE will have to assume that all dedicated pattersare activated.

According to a second embodiment of the present invention, the MIMO modeinformation is sent from the serving cell, i.e. the network node servingthe UE as in the first embodiment. However, in the second embodiment,the MIMO mode information comprises in addition to the informationwhether beamforming is used or not, information of the common referencesignal pattern with the smallest number of available common referencesignals. In case of only two common reference signal patterns, one bitis sufficient to indicate which one is used in a cell. Otherwise, N bitssignaling in e.g. PBCH maps to 2^(N) types of common reference signalpatterns. This will indicate to the UE which one of the possible 2^(N)common reference signal patterns is used in a cell. As the exactreference signal pattern (or details of such pattern) will bestandardized it is sufficient for the network to signal the index oridentity of the reference signal pattern used in that cell.

In the first and second embodiments, PBCH may be used to carry the MIMOmode information for the UE in idle mode since the UE does not read thePDSCH in idle mode. Similarly PDSCH may be used to carry the MIMO modeinformation when the UE is in connected mode since typically UE does notread PBCH in connected mode.

According to a third embodiment, a network node which is not the servingnode of the UE may map MIMO mode information on a pilot signal sent onthe synchronization channel (SCH). The SCH carries synchronizationsequences to the UE for acquiring frequency, time and cellsynchronization. In LIE the SCH comprises a primary synchronizationsequence (PSS) and a secondary synchronization sequence (SSS). The PSSis used to acquire OFDM symbol boundary. Thus more specifically the MIMOmode information can be mapped on SSS. In this way the UE can receiveinformation whether the neighbouring cell uses beamforming or not duringthe cell synchronization procedure. As an alternative, the MIMO modeinformation can also be mapped on the common reference signals i.e. onone or on a few hits sent on the part of common reference signals, whichare always present.

Furthermore, according to a fourth embodiment, the UE can read the MIMOmode information on a common channel, e.g. on the PBCH, sent from aneighbouring cell.

According to a fifth embodiment of the present invention, the third andfourth embodiments are combined. That implies that a UE first retrievesinformation from the pilot signal on the SCH of a neighbouring cell andif the UE can conclude that beamforming is being used by thatneighbouring cell, then the UE reads on the PBCH from said neighbouringcell to retrieve more detailed information associated with the MIMO modesuch that the UE can determine the available common reference signals tobe used for neighbour cell measurements by the UE.

Before performing the neighbour cell measurement from a cell (e.g. bymeans of an intra-frequency measurement, inter-frequency measurement, oreven inter-RAT measurement), the UE can either detect the PBCH (or anycommon channel carrying beamforming information) to retrieve theMIMO-mode related information (i.e. common reference signal patternindex) or can even be provided with this information by means of higherlayer signaling together with other information such as the frequency onwhich to measure.

In addition, it is also possible to indicate the available RS patternsthat are used in the neighbouring cells (for instance, 1 bit of RSpattern difference to indicate whether the patterns in neighbouringcells are the same as in the serving cell). The serving cell can acquireMIMO-mode related information of the neighbor cells via backhaulcommunication between itself and the neighbor cells. For instance ifsame MIMO is used in the serving and neighbor cells then the servingcell can indicate using 1 bit that the same RS pattern is used in theneighbor cells.

Based on this acquired information the UE can perform the measurementsbased on all the available reference signals that are used in that cellaccording to the embodiment of the present invention. The UE canbasically adapt the neighbour cell measurement filtering method oralgorithm according to the available reference signals in a cell. Whenbeamforming is used there will be fewer common reference signals formeasurements. This means measurements will incorporate more errorcompared to the scenario where a set of common reference signals aretransmitted. The measurements are done over a certain measurement periodto achieve the desired accuracy e.g. 200 ms when all common referencesignals are available. In case of reduction of common reference signals,the default measurement period may not be sufficient and would insteadtypically lead to measurement error or bias i.e. measured value wouldtypically be underestimated. The information whether beamforming is usedor not can assist UE to adapt the measurement period to compensate thebias or error of the measured value. A longer measurement period wouldallow the UE to obtain enough measurement samples to achieve the desiredmeasurement accuracy. For instance, in one scenario when beamforming isused, the UE can use more time domain filtering (i.e. a longermeasurement period such as 400 ms or even longer) to ensure that thebias is reduced. In another scenario, when no beamforming is used in thecell, the UE can use shorter time domain filtering or fewer samples or ashorter measurement period such as the default value (e.g. 200 ms). Thismeans that in the latter case the measurement will be done more quicklyand can reduce processing times in the UE as well. This will also saveUE power in DRX mode since fewer samples are needed compared to theworst case scenario i.e. under the assumption that the beamforming isemployed in all cells.

In accordance with embodiments described above, the MIMO modeinformation is sent on the PBCH (physical BCH) since it is easy for theUE to read the PBCH of the neighbour cell without much complexity. Inthis scenario the UE can read this information just after the cellsearch process i.e. after that it has identified this particularneighbour cell.

In case MIMO mode information is mapped on the pilot channel on thesynchronization channel (PSS/SSS) according to the third embodiment, theUE can acquire this information already during the neighbour cell searchprocedure. On the other hand, when the MIMO mode information is mappedon the set of common reference signals, which are always sent, the UEcan find this information during the neighbour cell measurement itselfor prior to it. If such information is mapped on D-BCH, which in turn issent via normal shared channel, the UE will also read it to acquire MIMOmode information after the cell search procedure.

In addition, the UE may assume that a certain MIMO mode setting is used.Hence, the network may or may not signal the MIMO mode patterninformation. The UE then performs measurements according to the assumedcommon reference signal pattern. The assumption can be based on somesort of autonomously detection of the presence of the common referencesignal pattern. For instance, the UE can check various possiblehypotheses by correlating over all possible common reference signalpatterns and locks on to the one which is found to be the most suitable.The UE may then also signal the measurements as well as the assumedsetting (i.e. index or identity of setting) used for measurements to thenetwork. If the signaled setting matches with the one actually used bythe network then no compensation is required. On the other hand if thereis a mismatch then the network can compensate for any errors by applyingan appropriate offset to the reported results.

FIG. 4 illustrates a UE 405 which is connected to radio base station400. The radio base station denoted 407 is serving a neighbouring cell.With reference to FIG. 4 , the radio base station 400 (also referred toas a network node) of a cellular communication network according toembodiments of the present invention enables a UE 405, to perform moreaccurate measurements, estimations or demodulations, since all availablecommon reference signals and/or dedicated reference signals can be used.The network node 400 comprises a first unit 401 configured to determineMIMO mode settings associated with the network node. It furthercomprises a second unit 402 configured to indicate, on a downlink commonor shared channel, the determined MIMO mode settings 406 to the UE. Theindicated MIMO mode settings 406 explicitly or implicitly indicateavailable common reference signals and/or dedicated reference signals tobe used for said UE measurements, estimations or demodulations. Asstated above, the UE measurements, estimations or demodulations compriseat least one of: neighbour cell measurement, channel estimation,demodulation and CQI estimation. The radio node may be a radio basestation as illustrated in FIG. 4 .

Furthermore, the UE comprises according to the present invention (inaddition to standard UE components such as RF components, differentfunctionalities implemented by software or hardware means) a receiver403 configured to receive an indication, on a downlink common or sharedchannel, of the determined MIMO mode settings 406, wherein the indicatedMIMO mode settings 406 explicitly or implicitly indicate availablecommon reference signals and/or dedicated reference signals to be usedfor said UE measurements, estimations or demodulations. The UE furthercomprises a unit 404 configured to perform measurements, estimations ordemodulations based on said received indication.

The present invention is not limited to the above-described preferredembodiments. Various alternatives, modifications and equivalents may beused. Therefore, the above embodiments should not be taken as limitingthe scope of the invention, which is defined by the appending claims.

The invention claimed is:
 1. A method in a network node of a cellularcommunication network of enabling a user equipment (UE) to performmeasurements, estimations or demodulations, the method comprising:determining Multiple Input Multiple Output (MIMO) mode settingsassociated with the network node used in at least one neighbor cell; andindicating, on a downlink common and/or shared channel, the determinedMIMO mode settings to the UE, wherein the indicated MIMO mode settingsexplicitly or implicitly indicate available common reference signalsand/or dedicated reference signals available for said UE measurements,estimations or demodulations, and wherein the determined MIMO modesettings are indicated in a common reference signal via one or both of:a single bit indicating a presence or absence of dedicated referencesignals, and a plurality of bits together containing an index or anidentity of the available dedicated reference signals.
 2. The method ofclaim 1, wherein the UE measurements, estimations or demodulationscomprise are selected from the group consisting of neighbor cellmeasurement, channel estimation, demodulation, and Channel QualityIndicator (CQI) estimation.
 3. The method of claim 1, wherein theindicated MIMO mode settings indicate whether beamforming is used ornot.
 4. The method of claim 1, wherein indicating the determined MIMOmode settings further comprises indicating the MIMO mode used in atleast one neighbor cell.
 5. The method of claim 1, wherein the indicatedMIMO mode settings further indicate the a bit pattern of the MIMOsetting with the a smallest number of available common referencesignals.
 6. The method of claim 1, wherein the network node is the aserving node for the UE.
 7. The method of claim 6, wherein the downlinkcommon or shared channel is a Broadcast Channel (BCH).
 8. The method ofclaim 6, wherein the downlink common or shared channel is a PhysicalDownlink Shared Channel (PDSCH).
 9. The method of claim 4 1, wherein theindicated MIMO mode settings further indicate whether the determinedMIMO mode settings of used in the at least one neighboring cell differor not from the MIMO mode settings of the a serving cell for the UE. 10.The method of claim 1, wherein the network node is not the a servingnode for the UE.
 11. The method of claim 1, wherein the downlink commonor shared channel is a Physical Broadcast Channel (PBCH).
 12. The methodof claim 10, wherein the downlink common or shared channel is aSynchronization Channel (SCH).
 13. The method of claim 1, wherein theindication of available common reference signals to be used for neighborcell measurements by the UE is transmitted via higher layer signaling.14. A method in a user equipment (UE) of enabling the UE to performmeasurements, estimations or demodulations, the method comprising:receiving an indication, on a downlink common and/or shared channel, ofdetermined Multiple Input Multiple Output (MIMO) mode settingsassociated with a network node used in at least one neighbor cell,wherein the indicated MIMO mode settings explicitly or implicitlyindicate available common reference signals and/or dedicated referencesignals available for said UE measurements, estimations ordemodulations, and wherein the indication is received in a commonreference signal, the indication comprising one or both of: a single bitindicating a presence or absence of dedicated reference signals, and aplurality of bits together containing an index or an identity of theavailable dedicated reference signals; and performing measurements,estimations, or demodulations based on said received indication.
 15. Themethod of claim 14, wherein the UE measurements, estimations ordemodulations are selected from the group consisting of: neighbor cellmeasurement, channel estimation, demodulation and Channel QualityIndicator (CQI) estimation.
 16. The method of claim 14, wherein theindicated MIMO mode settings indicate whether beamforming is used ornot.
 17. The method of claim 14, wherein the UE further receives theMIMO mode used in at least one neighbor cell.
 18. The method of claim14, wherein the indicated MIMO mode settings further indicate the a bitpattern of the MIMO setting with the a smallest number of availablecommon reference signals.
 19. A network node of a cellular communicationnetwork for enabling a user equipment (UE) to perform measurements,estimations, or demodulations, the network node comprising: a first unitconfigured to determine Multiple Input Multiple Output (MIMO) modesettings associated with the network node used in at least one neighborcell; and a second unit configured to indicate, on a downlink commonand/or shared channel, the determined MIMO mode settings to the UE,wherein the indicated MIMO mode settings explicitly or implicitlyindicate available common reference signals and/or dedicated referencesignals available for said UE measurements, estimations ordemodulations, and wherein the determined MIMO mode settings areindicated in a common reference signal via one or both of: a single bitindicating a presence or absence of dedicated reference signals, and aplurality of bits together containing an index or an identity of theavailable dedicated reference signals.
 20. The network node of claim 19,wherein the UE measurements, estimations or demodulations are selectedfrom the group consisting of: neighbor cell measurement, channelestimation, demodulation and Channel Quality Indicator (CQI) estimation.21. The network node of claim 19, wherein the indicated MIMO modesettings indicate whether beamforming is used or not.
 22. The networknode of claim 19, wherein the second unit is further configured toindicate the MIMO mode used in at least one neighbor cell.
 23. Thenetwork node of claim 19, wherein the indicated MIMO mode settingsfurther indicate the a bit pattern of the MIMO setting with the asmallest number of available common reference signals.
 24. The networknode of claim 19, wherein the downlink common or shared channel is aBroadcast Channel (BCH).
 25. The network node of claim 19, wherein thedownlink common or shared channel is a Physical Downlink Shared Channel(PDSCH).
 26. The network node of claim 22 19, wherein the indicated MIMOmode settings further indicate whether the determined MIMO mode settingsof used in the at least one neighboring cell differ or not from the MIMOmode settings of the a serving cell for the UE.
 27. The network node ofclaim 19, wherein the downlink common or shared channel is a PhysicalBroadcast Channel (PBCH).
 28. The network node of claim 19, wherein thedownlink common or shared channel is a Synchronization Channel (SCH).29. A user equipment (UE) operative to perform measurements, estimationsor demodulations, comprising: a receiver configured to receive anindication, on a downlink common and/or shared channel, of determinedMIMO mode settings associated with a network node used in at least oneneighbor cell, wherein the indicated MIMO mode settings explicitly orimplicitly indicate available common reference signals and/or dedicatedreference signals available for said UE measurements, estimations ordemodulations, and wherein the indication is received in a commonreference signal, the indication comprising one or both of: a single bitindicating a presence or absence of dedicated reference signals, and aplurality of bits together containing an index or an identity of theavailable dedicated reference signals; and a unit configured to performmeasurements, estimations or demodulations based on said receivedindication.